1. Field of the Invention
This invention relates to perpendicular magnetic recording media and more particularly to apparatus and methods for improving the writeability of perpendicular magnetic recording media.
2. Description of the Related Art
One of the primary challenges to increasing areal densities of magnetic recording media is overcoming the constraints imposed by the superparamagnetic effect. The superparamagnetic effect becomes significant when microscopic magnetic grains on the recording media become so small that they lose their ability to maintain their magnetic orientations. This condition may result in “flipped bits,” a condition where the magnetization of the bits suddenly and spontaneously reverses from north to south. Such a condition corrupts the data stored on the media, rendering the data as well as the storage device it is stored on unreliable and unusable.
In conventional longitudinal recording media, data bits are aligned horizontally, parallel to the surface of the disk. In perpendicular recording media, the data bits are aligned vertically, perpendicular to the disk. For example, referring to FIG. 1, a typical perpendicular recording device 100 may include a recording head 102 and a magnetic recording medium 104. The recording head 102 may include a write element 106, for writing magnetic signals to the recording medium 104, and a read element 108, to detect magnetic signals stored on the recording medium 104.
The magnetic recording medium 104 may include a magnetic recording layer 110, to store data, and a soft underlayer 112 to provide a return path for magnetic write fields generated by the write element 106. The magnetic recording layer 110 may comprise various magnetic grains each having a magnetic easy axis substantially perpendicular to the media surface, thereby allowing the grains to be vertically magnetized. When writing, the write element 106 generates a magnetic write field 116 that travels vertically through the magnetic recording layer 110 and returns to the write element 106 through the soft underlayer 112. In this manner, the write element 106 magnetizes vertical regions 114, or bits 114, in the magnetic recording layer 110. Because of the easy axis orientation, each of these bits 114 has a magnetization 118 that points in a direction substantially perpendicular to the media surface.
Because of the ability to utilize a soft underlayer in the perpendicular geometry, write fields generated by the perpendicular write element 106 may be substantially larger than conventional longitudinal recording write fields. This allows use of media 104 having a higher coercivity (Hc) and anisotropy energy (Ku), which is more thermally stable. Furthermore, unlike longitudinal recording, where the magnetic fields between two adjacent bits have a destabilizing effect, the magnetic fields of magnetization 118 of bits in perpendicular recording media 104 stabilize each other, enhancing the overall stability of perpendicular magnetic recording media even further. This allows for closer bit packing.
Referring to FIG. 2, as mentioned, one benefit of perpendicular recording is that the magnetic recording medium 104 is placed within the gap between the write element 106 and the soft underlayer 112, thereby allowing significantly higher write fields. When the write element 106 is writing the magnetic recording layer 110, the soft underlayer 112 reacts to the applied field of write element 106 in such a way that a mirror image 200 of the write element 106, or a secondary write pole 200, is generated in the soft underlayer 112. The write element 106 and the secondary write pole 200 together produce an apparent recording head 106, 200. In certain embodiments, the magnetic recording medium 104 may include an non-magnetic overcoat 202, above the magnetic recording layer 110, and an exchange break layer 204 to magnetically decouple the magnetic recording layer 110 from the soft underlayer 112.
One of the problem for conventional perpendicular media is that the magnetization 206, or magnetic easy axis 206, of the magnetic recording layer 110 is oriented nearly parallel to the magnetic field 116. This geometry has the disadvantage that relatively high reversal fields are necessary to reverse the magnetization 206 of the grains 208 of the magnetic recording layer 100 because little or no torque is exerted onto the grain magnetization 206 by the magnetic write field 116. Furthermore, such a nearly parallel alignment of field 116 and magnetization 206 has the additional disadvantage that the magnetization reversal time of the media grains 208 is increased. For these reasons, there have been proposals to produce magnetic media comprising magnetic grains having a magnetic easy axis that is tilted, or non-parallel, with respect to the surface normal. However, at the present time, apparatus and methods for producing high-quality recording media with a uniformly tilted easy axis do not exist.
Accordingly, what are needed are apparatus and methods for improving the writeability of perpendicular magnetic recording media. Further needed are apparatus and methods for producing perpendicular magnetic recording media that behaves like media with a tilted easy axis, while still being fully compatible with currently used processes and structures for producing perpendicular recording media. Such apparatus and methods are disclosed herein.